The present invention relates to trioctahedral phyllosilicates 2:1 of the stevensite or kerolite type containing fluoride, fluorinated in synthesis in an acid medium and modified post-synthesis to bring about the Si/Al and/or Mg/Al substitutions which impart acid properties to the solid.
These phyllosilicates may be incorporated in the composition of catalysts used to convert hydrocarbons, in particular for hydrocracking.
Phyllosilicates have a micro- or even meso-pore structure, attributable amongst other things to the nature, number and size of the compensation cations. The variation in the thickness of the space between sheets due to the exchange of compensation cations for other cations causes changes in properties. Phyllosilicates are used for adsorption and catalysis either as an active phase or as a means of assisting the active phase.
Due to the nature of the elements present in the tetrahedral and octahedral cavities and the nature of the compensation cations, the chemical composition of phyllosilicates is also an important factor affecting the selectivity of the exchange of cations, the adsorption selectivity and in particular the catalytic activity. This is explained by the nature and intensity of interactions between their internal and external surfaces on the one hand and with the adsorbed molecules on the other.
Numerous applications, particularly acid catalysis, require proton forms from which compensation cations introduced during synthesis have been completely removed. These forms may be obtained by one or more exchanges of these cations for NH4+ ions followed by calcination in order to generate the proton form.
Although the chemical bonds between the elements in the structure of phyllosilicates are ion-covalent, they will be assumed to be ionic here in order to simplify the description. Starting from a presentation in which the O2xe2x88x92 ions are in one plane, in contact with one another, in the most compact manner, it is possible to obtain a plane having hexagonal cavities, referred to as a hexagonal plane, by removing one O2xe2x88x92 ion in two from one of every two rows of O2xe2x88x92 ions. The structure of a phyllite may be simply represented using arrangements of hexagonal planes of O2xe2x88x92 ions and compact planes of O2xe2x88x92 and OHxe2x88x92 ions. The OHxe2x88x92 ions fill the cavities in hexagonal planes of O2xe2x88x92 ions. Placing two compact planes one on top of the other bounded on either side by a hexagonal plane enables an octahedral layer (O) to be defined between 2 tetrahedral (T) layers, hence the name TOT sheet. Such an arrangement, also referred to as 2:1, enables a layer of octahedral cavities to be defined, located between two layers of tetrahedral cavities. Each tetrahedron has one O2xe2x88x92 ion in common with the octahedral layer and each of the other three O2xe2x88x92 ions is shared with another tetrahedron in the same tetrahedral layer.
The crystal lattice is therefore made up of six octahedral cavities having four tetrahedral cavities on either side. If the octahedral sites are occupied by divalent cations, this will be referred to as a trioctahedral phyllosilicate 2:1. In the case of a phyllosilicate made up of the elements Si, Mg, O and the OH group, such an arrangement corresponds to the formula Si8Mg6O20(OH)4. The tetrahedral cavities contain the silicon element and the octahedral cavities the magnesium element. Such a formula corresponds to the natural product known as talc.
If a very small fraction of octahedral cavities are unoccupied, a lack of positive charge appears within the structure. This lack of charge will be compensated by the presence of exchangeable compensation cations located in the interlayer space. In the case of a phyllosilicate made up of the elements Si, Mg, O and the OH group, the formula of such a compound may be written as follows for a lattice
C2/zmm+Si8(Mg6xe2x88x92zxe2x96xa1z)O20(OH)4 
where xe2x96xa1 represents an unoccupied octahedral cavity, i.e.
MgzSi8(Mg6xe2x88x92zxe2x96xa1z)O20(OH)4 or Na2zSi8(Mg6xe2x88x92zxe2x96xa1z)O20(OH)4 
if the exchangeable cation C corresponds to the magnesium or sodium element respectively.
The structural group [Si8(Mg6xe2x88x92zxe2x96xa1z)O20(OH)4]2zxe2x88x92 for a lattice or [Si4(Mg3xe2x88x92zxe2x96xa1z)O20(OH)2]2zxe2x88x92 for a half lattice corresponds to a natural smectite known as kerolite if z is very close to zero and stevensite if z if higher. Generally speaking, it is not uncommon in the natural product for Mn(II) and Fe(II) ions to be present alongside the magnesium cation in the octahedral cavity.
It is not easy to understand why trioctahedral phyllosilicate 2:1 should be lacking in positive charges in the octahedral layer, currently known under the name of stevensite, as distinct from the products cited in background literature. Its occurrence in nature has been the subject of controversy, because some regard phyllosilicate as a variety of talc. The fact that its chemical composition is close to that of talc goes a long way towards explaining this. Natural stevensite occurs in veins or pockets, mixed to a greater or lesser degree with other phases, which may explain the difficulties encountered when attempting to characterise or sample it. However, progress in the systematic classification of natural phyllosilicates and improved analysis of samples has improved what we know about their characteristics.
Until now, the Si/Al or Mg/Al combination has been produced by synthesis or, in the case of minerals of the smectite type, by a cationic exchange with aluminium in order to adjust the Si/Al and Mg/Al ratios to improve the stability of materials, these exchanges being effected in the absence of any fluoride ion (patent JP 94-191549).
The present invention relates to stevensite or kerolite trioctahedral phyllosilicates 2:1 containing fluorine and having inter-sheet Mg2+ cations, fluorinated in synthesis in an acid medium and modified post-synthesis in the presence of fluorine, said post-synthesis fluorination consisting in incorporating aluminium in the structure of the stevensite or kerolite (Mg), i.e. producing a substitution of the silicon and/or magnesium elements by the aluminium. The advantage of this method is that it enables the acidity of the phyllosilicate proposed by the invention to be increased in a controlled manner.
Another objective of the present invention is to propose a method of preparing said phyllosilicates and their use for converting hydrocarbons.
The phyllosilicates proposed by the invention are obtained by processing, post-synthesis, stevensite or kerolite type trioctahedral phyllosilicates 2:1 immediately after synthesis, and these are synthesised in a fluoride medium (for example in the presence of HF acid or any other acid source of fluoride ions and/or any other source of fluoride ions).
The general chemical formula (for a half lattice) of the initial phyllosilicates is as follows:
C2z/mm+Si4(Mg3xe2x88x92zxe2x96xa1z)O10(OH)2xe2x88x92uFu,nH2O 
where
C is the compensation cation from the reaction medium constituted at least partially by the Mg2+ cation or a cation introduced by at least one process of post-synthesis ion exchange, selected from the group consisting of the cations of elements from groups IA, IIA and VIII of the periodic table, the cations of rare earths (cations of elements having an atomic number 57 to 71 inclusive), the ammonium cation, organic cations containing nitrogen (among which are alkylammonium and arylammonium),
m is the valence of the cation C,
z is a number greater than 0 and less than or equal to 1, preferably ranging between 0.01 and 1,
u is a number greater than 0 and less than or equal to 1, preferably ranging between 0.01 and 2,
n is a real positive number and not zero,
and xe2x96xa1 stands for an octahedral cavity.
The magnesium element may be partially substituted by at least one of the elements from the group consisting of nickel, cobalt and zinc, these elements being taken from the reaction medium.
The X-ray diffraction diagram of a purely magnesium-based trioctahedral phyllosilicate 2:1 is characterized by the presence of the following rays:
a ray corresponding to a value of d060 equal to 1.52xc2x10.01xc3x9710xe2x88x9210m
two other rays corresponding to values of dhkl equal to 4.53xc2x10.05xc3x9710xe2x88x9210m and 2.56xc2x10.05xc3x9710xe2x88x9210m
at least one reflection 001 such that d001 is between 10.1 and 21.5xc3x9710xe2x88x9210m in accordance with the chemical formula of said phyllosilicates. This reflection enables a distinction to be made between trioctahedral phyllosilicate 2:1 of the kerolite type and trioctahedral phyllosilicate 2:1 of the stevensite type. A low value, somewhat less than 11xc3x9710xe2x88x9210m corresponds to trioctahedral phyllosilicate 2:1 of the kerolite type and a highter value, somewhat higher than 11xc3x9710xe2x88x9210m corresponds to trioctahedral phyllosilicate 2:1 of the stevensite type.
Stevensite or kerolite type trioctahedral phyllosilicate 2:1 also exhibits at least one signal during analysis of the fluorine 19F by Nuclear Magnetic Resonance with Magic Angle Rotation (NMR-MAR), determined and known by the person skilled in the art. The chemical displacement of this signal depends on the composition of the octahedral layer. The NMR-MAR 19F spectrum of stevensite or kerolite type trioctahedral phyllosilicate 2:1 containing magnesium in the octahedral layer is characterised by an intense double signal centred on xe2x88x92175.0 and xe2x88x92176.6 ppm. A breakdown of this signal highlights two shoulders at xe2x88x92178.0 and 181.0 ppm.
The stevensite or kerolite type trioctahedral phyllosilicate 2:1 proposed by the invention is characterised by gaps in the octahedral layer, evidenced by specific swelling properties. In effect, the swelling properties observed on the raw synthesis product disappear after heating for 12 h at 250xc2x0 C. The X-ray diffraction diagram for stevensite or kerolite type trioctahedral phyllosilicate 2:1 when heated then exhibits a periodicity d001 corresponding to that of a talc with an imperfect organisation. Under NMR-MAR analysis of the fluorine 19F, the probe used in the octahedral layer, the spectrum of the phyllosilicate proposed by the invention and based purely on magnesium, heated to 250xc2x0 C. for 12 h, will have only one signal centred on xe2x88x92176.6 ppm which can not be broken down. This chemical displacement is attributed to the F(3 Mg) atoms, corresponding to fluorine atoms having three Mg in their environment. The Mg2+ cations present as compensation cations have migrated during heating to occupy the gaps in the octahedral position. The product obtained after heating no longer contains compensation cations.
The trioctahedral phyllosilicate 2:1 prepared as proposed by the invention is therefore of the stevensite or kerolite type.
The trioctahedral 2:1 phyllosilicates proposed by the invention are produced from phyllosilicates synthesised in a fluoride medium in the presence of the acid from HF acid or any other acid source of fluoride ions and/or any other source of fluoride ions and having a pH less than or equal to 7, and preferably between 0.5 and 6.5. The presence of the element F enables trioctahedral phyllosilicates 2:1 to be obtained in the absence of alkaline cations. They are then put through a post-synthesis treatment in a fluoride medium in the presence of HF acid or any other acid source of fluoride ions and/or any other source of fluoride ions.
For the purpose of the invention, the general chemical formula (per half lattice) of phyllosilicates containing fluorine, magnesium and aluminium is of the type:
C(2(3xe2x88x92txe2x88x92y)+xxe2x88x92y)/mm+(Si4xe2x88x92xAlx)(MgtAlyxe2x96xa13xe2x88x92txe2x88x92y)O10(OH)2xe2x88x92zFz,nH2O 
where
C is the compensation cation taken from the reaction medium or a cation introduced by at least one post-synthesis ion exchange process, selected from the group consisting of the cations of elements from groups IA, IIA, IIB and VIII of the periodic table, the cations of rare earths (cations of elements having an atomic number 57 to 71 inclusive), the ammonium cation, the organic cations containing nitrogen (among which are alkylammonium and arylammonium).
m is the valence of the cation C,
t is a number ranging between 0 and 3,
x is a number greater than 0 and less than or equal to 1,
y is a number greater than 0 and less than or equal to 2,
z is a number greater than 0 and less than or equal to 2,
n is a real positive number and not zero.
The compensation cation is generally magnesium.
The magnesium element may be substituted in part or in full by at least one of the elements from the group consisting of nickel, cobalt and zinc, these elements being taken from the reaction medium.
The X-ray diffraction diagram phyllosilicate 2:1 obtained by the method described above is characterized by the presence of the following rays:
one of more rays corresponding to a value of d060 equal to:
1.52xc2x10.01xc3x9710xe2x88x9210m, attributable to the trioctahedral character,
1.50xc2x10.01xc3x9710xe2x88x9210m, attributable to the di-trioctahedral character,
1.49xc2x10.01xc3x9710xe2x88x9210m, attributable to the dioctahedral character,
at least one reflection 001 such that d001 is between 10.1 and 17.0xc3x9710xe2x88x9210 m in accordance with the chemical formula of said phyllosilicates.
It may also exhibit other rays corresponding to values of dbkl equal to
4.53xc2x10.01xc3x9710xe2x88x9210m,
3.16xc2x10.01xc3x9710xe2x88x9210m,
2.56xc2x10.01xc3x9710xe2x88x9210m
1.72xc2x10.01xc3x9710xe2x88x9210m
After said post-synthesis treatment with aluminium, the solid proposed by the invention can be characterised under NMR-MAR 19F analysis by one or two new signals, depending on the processing conditions (duration, temperature, composition of the reaction mixture), centred on xe2x88x92152.0 and xe2x88x92132.0 ppm. These two displacements are attributed to the F(Mg,Al,xe2x96xa1) and F(2A,xe2x96xa1) atoms respectively.
The NMR-MAR of 29Si enables the tetrahedral layer to be characterised. The spectrum of the stevensite or kerolite, containing only silicon in the tetrahedral layer, is characterised by a signal centred on xe2x88x9295.0 ppm. This chemical displacement is attributed to the Si(3Si) or Q3(0Al) atoms. After post-synthesis treatment with aluminium, the solid proposed by the invention is characterised by one or more signals, depending on the treatment conditions (duration, temperature, composition of the reaction mixture). These new signals are centred on xe2x88x9293.5, xe2x88x9292.6 and xe2x88x9288.1 ppm. These chemical displacements are attributed to Si(3Si) or Q3(0Al) atoms, to Si(2Si, 1 Al) or Q3(1Al) atoms and to Si(1Si, 2A1) or Q3(2Al) atoms. By ascertaining the different contributions, it is then possible to calculate the tetrahedral substitution rate using the formula known to the person skilled in the art. The tetrahedral substitution rate (x) varies depending on the processing duration and temperature.
Finally, the solid proposed by the invention is characterised under NMR-MAR analysis of the aluminium 27Al by a signal centred on 0 ppm. This chemical displacement is attributed to the aluminium in the tetrahedral layer.
The phyllosilicates obtained after said post-synthesis treatment proposed by the invention have an adjustable acidity which, determined by ammonia adsorption, corresponds to a value in excess of 1.2 m2/100 g of clay calcined at 1000xc2x0 C. The acidity of the stevensite or kerolite type phyllosilicate prior to post-synthesis modification is less than 0.70 m2/100 g of clay calcined at 1000xc2x0 C.
The invention also relates to a method of preparing said stevensite or kerolite type trioctahedral phyllosilicates 2:1 proposed by the invention, which consists in:
a) forming a reaction mixture in aqueous solution having a pH less than 7, containing in particular water, at least one source of the silicon element, at least one source of the magnesium element and at least one source of fluorine.
In terms of molar ratio, said mixture has a composition within the following value ranges:
0 less than Mgtotal/Sixe2x89xa650, preferably 0 less than Mgtotal/Sixe2x89xa610, and advantageously at least equal to 0.01,
0 less than Fxe2x88x92total/Sixe2x89xa610, preferably 0 less than Fxe2x88x92total/Sixe2x89xa68, preferably at least equal to 0.01,
0xe2x89xa6HF/Sixe2x89xa610, preferably 0 less than HF/Sixe2x89xa68, preferably at least equal to 0.01,
5xe2x89xa6H2O/Sixe2x89xa6500, preferably 10xe2x89xa6H2O/Sixe2x89xa6300.
Fxe2x88x92total represents the sum of Fxe2x88x92 ions from all the fluoride sources and in particular HF acid or any other acid source of fluoride ions and/or any other source of fluoride ions, in particular MgF2 and H2SiF6. Mgtotal represents the sum of Mg+2 ions from all the sources of the magnesium element and optionally MgF2 if MgF2 is used alone or partially as the source of Fxe2x88x92 ions. The magnesium source may be mixed with or totally substituted by at least one source of the elements from the group consisting of cobalt, zinc and nickel.
Advantageously, said reaction mixture is prepared so as to have a pH ranging between 0.5 and 7, and preferably between 0.5 and 6.5.
In a preferred approach to preparing trioctahedral phyllosilicates 2:1 as proposed by the invention, the molar ratios of the constituents of the reaction mixture are within the following value ranges:
0 less than Mgtotal/Sixe2x89xa63,
0 less than Ftotal/Sixe2x89xa66,
0xe2x89xa6HF/Sixe2x89xa60.6,
40xe2x89xa6H2O/Sixe2x89xa6500.
As an option, it is also possible to work accompanied by stirring and optionally in the presence of seeds of trioctahedral phyllosilicate 2:1 crystals.
The pH of the reaction medium, which is below 7, may be obtained directly using one or more reagents, or by adding an acid.
Numerous sources may be used for the silicon element, which might include, by way of example, silica in the form of hydrogels, aerogels, colloidal suspensions, silica produced by precipitating soluble silicate solutions or by hydrolysis of silica esters such as Si(OC2H5)4, silica prepared by treatments to extract natural or synthetic compounds such as aluminium silicates, aluminosilicates, zeolites.
Among the sources for the magnesium element, for example, it is possible to use the oxide MgO, the hydroxide Mg(OH)2, the salts such as magnesium chloride, fluoride, nitrate and sulphate, organic acid salts. The same types of source may be used for the nickel, cobalt and zinc elements if these partially substitute the magnesium.
Instead of using separate sources for the various elements mentioned above, it would also be possible to use sources combining at least two of the elements.
b) said reaction mixture is maintained at a temperature below 250xc2x0 C. and preferably below 220xc2x0 C., preferably in an autoclave, the interior of which is advantageously coated with polytetrafluoroethylene, for a period which may vary from a few hours to a few days depending on the reaction temperature, until a crystallised compound is obtained which is advantageously separated from the parent waters before being washed with distilled water and then dried.
c) the aluminium is incorporated by post-synthesis treatment, by placing the phyllosilicate in stevensite or kerolite form in contact with an aluminium source in the presence of fluorine in an autoclave heated to a temperature ranging between 100 and 250xc2x0 C. for periods ranging between 2 and 2000 h.
Incorporating the aluminium element in the structure of the stevensite or kerolite(Mg), by bringing about the Si/Al and/or Mg/Al substitutions, enables its acid properties to be enhanced and, by the same token, its catalytic properties for acid catalysis.
The reaction medium is prepared by mixing the various reagents at ambient temperature whilst stirring. The various reagents may be introduced in any order. By preference, they are added in the following order: distilled water, fluorine source, aluminium source and stevensite or kerolite.
Numerous sources may be used for the aluminium element, examples of which are aluminium isopropoxide [Al((CH3)2COH)3] (IsoAl), pseudo-boehmite (AlOOH), preferably pseudo-boehmite. The fluorine sources may be selected from NaF, NH4F and HF.
In a preferred embodiment, after a brief period of curing (several minutes), the mixture is decanted into an autoclave (for example of stainless steel lined with a coating of polytetrafluoroethylene). The autoclave is heated to a temperature ranging between 110 and 170xc2x0 C. The processing time represents the time during which the autoclave is maintained at temperature and under pressure. It may vary between 2 h and 2000 hours. The autoclave is cooled to ambient temperature. After opening, the solid phase is separated by filtering the liquid phase and is then washed with distilled water and dried.
The octahedral (Mg/Al) and tetrahedral (Si/Al) substitution rates are controlled by acting on the processing temperature and duration.
In order to make it easier to define the composition of the reaction mixture at step c) of post-synthesis modification, the notation system used is as follows:
The theoretical quantity of fluorine needed to expel all the magnesium (octahedral and inter-sheet) contained in the kerolite or stevensite type trioctahedral phyllosilicate 2:1 is written Fth. It is 0.015 mole for 1 g of phyllosilicate, given that Mg is expelled in the form of MgF2. This value is calculated using the general chemical formula per half-lattice of the phyllosilicate, C2z/mm+Si4(Mg3xe2x88x92zxe2x96xa1z)O10(OH)2xe2x88x92uFu,n H2O, assuming z=0.
The total quantity of fluorine introduced into the reaction mixture at step c) is written Ft.
The theoretical quantity of aluminium needed to ensure that the MG/Al is substituted in full (3Mg2+⇄2Al3+), is written Alth. It is 5.25xc3x9710xe2x88x923 mole of aluminium for 1 g of phyllosilicate.
The parameter denoting the molar ratio of the quantity of hydrofluoric acid to the quantity of sodium fluoride and hydrofluoric acid is denoted by:   S  =      HF          HF      +      NaF      
a is the ratio Al/Alth 
f is the ratio Ft/Fth.
Said reaction mixture corresponding to step c) has a composition such that:
S is between 0 and 1
a is between 0 and 30 and more preferably between 2 and 15
f is between 0 and 1, 0 being excluded,
i.e.
Al2O3/SiO2: 0.3 to 5,
H2O/SiO2: 140 to 265,
Ft/SiO2: 0 to 2 (0 excluded)
and, if HF and/or NaF is used:
HF/SiO2: 0 to 2,
NaF/SiO2: 0 to 2,       HF          HF      +      NaF        =      0    ⁢          xe2x80x83        ⁢    to    ⁢          xe2x80x83        ⁢    1.  
Surprisingly, the quantity of fluorine introduced into the reaction mixture has been found to affect the tetrahedral substitution rate (x) and the octahedral substitution rate (y). If using the sodium fluoride alone, the results obtained are close to those obtained using hydrofluoric acid alone. However, sodium fluoride enables a higher rate of tetrahedral substitution to be obtained.
If two fluoride sources are used, the tetrahedral substitution rate (x) varies randomly depending on the HF/NaF+HF ratio, the total quantity of fluorine being maintained constant. The HF/NaF+HF ratio, on the other hand, has a surprising effect on the octahedral substitution rate.
The trioctahedral phyllosilicates 2:1 proposed by the invention may be used alone or as a mixture with a matrix, such as catalysts used to convert hydrocarbons, in particular for hydrocracking.
The matrices used are usually selected from the group consisting of alumina, silica, magnesia, titanium oxide, zirconium, combinations at least two of these compounds and the alumina-boron oxide combinations.
The matrix is preferably selected from the group consisting of silica, alumina, magnesia, silica-alumina mixtures and silica-magnesia mixtures.
The catalyst will then have a content by weight of stevensite or kerolite type trioctahedral phyllosilicate 2:1 proposed by the invention which is advantageously in the range of between 10 and 99.5%.
The catalyst containing the phyllosilicate proposed by the invention will additionally contain a hydrogenating or dehydrogenating function, generally constituted by at least one metal and/or metal compound selected from groups IA, VIB and VIII of the periodic table, for example platinum, palladium and/or nickel.
For hydrocracking applications, the charges used in the method are, for example, gas oils, gas oils under vacuum, residues with the asphalt removed or hydro-treated or equivalent. These may be heavy cuts constituted by at least 80% by volume of compounds whose boiling point is in excess of 350xc2x0 C. and preferably less than 580xc2x0 C. They generally contain heteroatoms such as sulphur and nitrogen. The nitrogen content is usually between 1 and 5000 ppm by weight and the sulphur content between 0.01 and 5% by weight. The hydrocracking conditions such as temperature, pressure, hydrogen recycling rates, hourly velocity by volume, may vary depending on the nature of the charge, the quality of the desired products and the installations used by the refiner.
Temperatures are generally in excess of 230xc2x0 C. and commonly between 300xc2x0 C. and 480xc2x0 C., preferably less than 450xc2x0 C. The pressure is greater than or equal to 2 MPa and in general higher than 3 MPa, even 10 MPa. The hydrogen recycling rate is a minimum of 100 and commonly between 260 and 3000 liters of hydrogen per liter of charge. The hourly velocity by volume is generally between 0.2 and 10 hxe2x88x921.
The following examples illustrate the invention but without limiting its scope.